Present invention relates to an image processing method and apparatus which performs quantization for pseudo-halftone outputting.
Generally, the average error minimization method, which is substantially the same as the error diffusion method, is known as one of the density-conservation type binarization methods. The error diffusion method executes level conversion by diffusing errors generated during level conversion to peripheral pixels of a pixel of interest.
On the other hand, in TV image reception, interlaced scanning is used, as an image output method, to reduce flicker in an image using a CRT and to narrow transmission band. The interlaced scanning forms one image frame with two separate transmission fields, i.e., an odd-numbered field (referred to as "D1 field") and an even-numbered line field (referred to as "D2 field") to be interposed at the receiver. The D1 and D2 fields are transmitted and displayed consecutively, thus completing a picture for one frame.
The interlaced scanning is applicable to a display which basically performs binary representation. However, problems occur when the error diffusion method is used to attain pseudo-halftone image output.
The error diffusion method conserves density by diffusing a conversion error to peripheral pixels adjacent to the pixel of interest. If this conventional error diffusion is applied to the interlaced scanning which interlaces two image data each having alternate lines, error diffusion cannot work between the separated D1 and D2 fields. This results in failure of density conservation, thus degrading image quality.